In the field of robotic devices there is a need for joint structures that connect robotic limbs or components that will permit precision controlled rotation in three planes. This is also a desirable feature for joint prosthesis for replacing a diseased or damaged joint between human body skeletal members where the joint prosthesis should simulate the durable and resilient characteristics of the joint it replaces as well as duplicate the rotational movement and flexibility of the replaced joint.
There are numerous prior art devices that disclose prostheses for the replacement of knee, elbow, hip and knuckle joint but problems have been encountered with each type of design. Usually the joint protheses have hinging elements formed with metal-to-metal or metal-to-plastic bearing elements such that insufficient resiliency or flexibility is provided at the hinging element to cushion and absorb impact loads or lateral and compressive loads that are applied to the joint in every day use. Thus, the joints eventually fail and have to be replaced.
To combat the problem of insufficient resiliency or flexibility some devices have been proposed in which the prosthesis is formed almost entirely of a flexible member such as an elastomer. Problems have occurred here in that shear forces over a period of time cause the elastomer to tear resulting in the eventual failure of the prosthesis. Also if the elastomer is too flexible or becomes more flexible due to prolonged use, the skeletal components have sometimes become dislocated resulting in failure.
For robotic devices there are other problems. Conventional robot arms are built up from a number of elements and joints, which besides the tool and the load also must support the equipment for the motion and power generation for the separate elements. This equipment usually comprises pneumatic or hydraulic cylinders, electric motors etc., which means that the elements and the joints have to be relatively coarse or heavy in order to support the equipment. Thus the robot will have a bulky shape and comparatively large external dimensions, which will reduce the flexibility of the robot arm.
There are robotic couplings available that use cable but there do not appear to be any in the prior art that disclose the controlled use of the cable to allow precise and predetermined control of the compliance flexibility and rotational movement of the robotic joint in three planes, as well as absorb heavy loads.